pp32 is a member of a highly conserved gene family that includes pp32, pp32rl, pp32r2, and APRIL. pp32 is a tumor suppressor that is generally nuclear, but is capable of shuttling between the nucleus and cytoplasm. In normal tissues, it is found principally in cell populations with potential for self-renewal and certain longlived neuronal cell populations. Certain normal populations such as activated CD34+ stem cells additionally express pp32rl and/or pp32r2, as do human prostatic and breast adenocarcinomas and cell lines derived from human epithelial and lymphoid neoplasms. APRIL was isolated as part of the complex with HuR. A number of clinical studies suggest that pp32, pp32rl, and pp32r2 may be useful markers in establishing the diagnosis and prognosis of breast, prostate, and other cancers, however progress in this area is limited by the lack of antibodies that distinguish among gene family members. The hypothesis underlying this proposal is that pp32 gene family expression and characterization will be a useful early detection marker in cancer since pp32, pp32rl, and pp32r2 expression is elevated in a high percentage of human breast and prostate cancers. Monoclonal antibodies distinguishing among family members will be required to construct practical and commercially viable clinical assays. The specific aims of this proposal are: 1. To generate monoclonal antibodies to pp32, pp32rl, pp32r2, and APRIL. Recombinant pp32, pp32rl, and pp32r2 have already been generated and will be used as immunogens for monoclonal antibody production. APRIL will be cloned into a vector that will express it as a GST fusion protein with a cleavable site. Clones will be screened for differential reactivity with pp32 family members in several assay formats. 2. To produce the monoclonals and formulate them into clinically useful assays. Immunohistochemical, flow cytometric, immunoblot, and ELISA assays will be developed for future clinical evaluation.